1. Field of the Invention
This invention relates to a power supply for a power circuit and, more particularly, to a power supply which generates a power output from one or more input power lines.
2. Background Information
Various electrical and electronic systems utilize control direct current (DC) power derived from a variety of alternating current (AC) and DC input line voltages. For example, a nominal AC line voltage may be 110/120 VAC, 240 VAC, 480 VAC, or 575 VAC. Under normal operation, typical variations in these AC line voltages may present a wide range of possible input AC line voltages (e.g., about 60 through about 632 VAC). It is believed that such a wide voltage range has been addressed by a variety of different power supply designs, or configurations thereof, each of which is associated with a subset of this range of possible AC line voltages.
Furthermore, the AC line voltage may be single phase or plural phase (e.g., three phases). Moreover, AC line voltages may have a wide frequency range (e.g., 40 through 400 Hz). DC line voltages, of course, have a zero frequency.
Prior art power supplies have typically addressed the variety of AC line voltages with line frequency control power transformers and rectification circuits. However, such designs have been complicated by: (1) the variable number of phases (e.g., a single phase requires a greater volt-amp (VA) capacity while plural phases require plural transformer windings); (2) the variable line frequency (e.g., a relatively small change in line frequency from 60 Hz to 50 Hz requires about 16% more transformer mass); and (3) the variable line voltage (e.g., multiple transformer taps and associated jumpers are required). Furthermore, power transformers which input the AC line voltages preclude the input of a DC line voltage thereto.
Whenever surge waveforms must be suppressed from the line voltages, a power supply design is further complicated. In typical power supply surge tests, a power supply must operate without failure or interruption of its output voltage. The ANSI C62.41 surge waveform, for example, includes a 6 KV peak open circuit voltage output from a 2 ohm voltage source with a 1.2 .mu.s rise time and a 50 .mu.s fall time to 50% of the peak voltage output, and with a 3 KA peak short circuit current output with an 8 .mu.s rise time and a 20 .mu.s fall time to 50% of the peak current output. Although a simple single phase power transformer may typically be protected from a surge waveform by the addition of extra transformer insulation, requirements for plural phases, plural taps and the requisite terminations thereto present further opportunities for arcing and damage by the surge waveform.
A power supply design is even further complicated when the surge withstand capability requirement is coupled with the requirement for a wide range of line voltage magnitude and frequency. For line voltages having a possible 10:1 voltage variation, the power dissipation in some components varies by a factor of 100:1. For example, the power-up of a pulse-width modulation (PWM) controller is very difficult. If a resistor-zener combination is used to power the PWM controller, then a 100:1 change in power dissipation will occur at the resistor. In a circuit with a 5K .OMEGA. resistor, a 10 V zener and a running bias of about 10 mA, for example, the resistor would dissipate about 0.5 W at a relatively low 60 VDC input line voltage. However, at a relatively high 600 VDC input line voltage, for example, the resistor's power dissipation would increase to about 70 W.
There is a need for an improved single power supply which accepts a wide range of input line voltages.
There is a more particular need for such a power supply which accepts both AC and DC input line voltages.
There is an even more particular need for such a power supply which accepts a wide range of AC input line voltages over a wide range of line frequencies in addition to comparable magnitude DC input line voltages.
There is a still more particular need for such a power supply which provides substantial protection from surge waveforms on the input line voltages.